1. Field of the Invention
The present invention relates to a water treatment system and process and, more particularly, to a water treatment system and process for producing purified water for human consumption.
2. Description of the Related Art
Purified water is used in many industries including the chemical, foodstuffs, electronics, power, medical and pharmaceutical industries, as well as for human consumption. Typically, prior to use in any one of these fields, the water is treated to reduce the level of contaminants to acceptable levels. These treatment techniques include disinfection, distillation, filtration, ion exchange, reverse osmosis, photooxidation, ozonation, and combinations thereof.
Various levels of purity may be required for different end uses. Water quality may be regulated by various government agencies and trade organizations including the U.S. Environmental Protection Agency (EPA) and the Food and Drug Administration (FDA).
The beverage industry consumes a significant amount of water that must meet environmental, as well as health requirements. In addition to regulations that assure that beverages are safe for consumption, the beverage industry faces additional standards that are grounded in quality control. For example, a water supply that meets federal regulations for microorganisms may not satisfy a beverage producer's quality control standards for additional parameters such as taste and odor that may affect product quality. These standards may include hardness (calcium, magnesium and silica content), bicarbonate, pH, total suspended solids (TSS), total dissolved solids (TDS), color, taste, and temperature.
Control of these parameters is complicated by the decentralized structure of the beverage industry itself. For instance, a world-wide producer of beverages typically has a number of points of production throughout the world. Each of these points may access a water supply that is different than those used by other plants. Although federal regulations may help to standardize health and safety requirements for water used in beverage production in the United States, these standards may differ greatly from those in other countries. These different standards may impact factors such as taste, odor, and appearance. This may be important to producers who market a beverage under a single trademark throughout a large territory. For example, a customer who consumes a beverage in one part of the country will expect the same appearance and taste from that beverage regardless of where it is purchased. To assure this type of consistency, the beverage producer may require that the water used in beverage production meet the same, or similar standards, regardless of where the beverage is produced. One way of achieving this goal is through the use of water treatment processes.
Assuring water quality for a number of bottling plants typically requires the imposition of measurable and attainable water quality standards that can be achieved at minimal cost for various types of feed water that may be used. These quality control issues become even more difficult to implement and control when fountain outlets are included. Fountain outlets are typically those locations where beverages are produced for immediate on-site, or nearby, consumption. Generally, at a fountain outlet, water is mixed with a flavor syrup and, in the case of carbonated beverages, carbon dioxide. The beverage may then be served directly to the consumer. Among the advantages provided by fountain outlets are the savings realized from not shipping or storing a bulky product. Because of these and other advantages, millions of licensed fountain outlets are in operation worldwide.
Consumers typically expect consistent quality in their beverages whether they choose to purchase a can or bottle from a store, or a cup from a fountain outlet. As water quality can affect the taste and appearance of a beverage, it is important for beverage licensors to provide water quality standards for fountain outlets as well as for bottlers. There are several factors that may influence water quality standards for fountain outlets, two of which are available sources of water and the cost of treating the water.
As fountain outlets may exist in various locations, the water sources used to produce fountain beverages may also differ. These water sources may include, for example, municipal water supplies, surface water, well water, precipitated water and desalinated sea water. Each of these sources may supply water of varying quality, and even within one type of water supply, for instance, well water, the type and quality of the water supplied may not be consistent from location to location.
Additionally, fountain outlets are commonly found at restaurants, snack bars, convenience stores, and the like, and at many of these locations the cost of water treatment may have an impact on profitability. Thus, beverage producers and licensors must balance the needs of the consumer for consistent taste and appearance with the outlet's need for a low-cost water supply. In addition, the outlet operator is concerned with reliability; if the water treatment system fails, beverage production at a fountain outlet comes to a halt. System maintenance is also important and typically the goal is for less frequent maintenance with less complicated procedures.
The capacity of the water treatment system is also different from that required by a bottler. Typically, the output requirements are much lower at fountain outlets, yet the system must still be able to produce an adequate supply of high quality water at times of peak demand, and since fountain outlets may go through periods of non-use, a water treatment system should be able to supply high quality water on demand after a period of non-use.
Different well water sources may provide a challenge for those designing water treatment systems for fountain outlets. Well water may contain high concentrations of dissolved matter, such as bicarbonate and dissolved solids, as well as suspended material that may contribute to taste and appearance. For example, water may be hard, having a high concentration of calcium, magnesium or silica and may contain additional ionic materials contributing to total dissolved solids (TDS). In addition, organic materials, as well as dissolved gases, may be present, pH and buffering capacity may vary widely, and the composition of the water from a single well may vary over time or with different levels of use.
Various water treatment systems and processes exist for producing high purity water for use in beverage production and other industries. Among these systems are disinfection units, such as chlorinators and ozonators, filters, water softeners, reverse osmosis systems, and chemical ion exchange devices.
Disinfection units are typically used to reduce the concentration of viable microorganisms in a water supply. This may be accomplished by adding a disinfectant, for example, chlorine, ozone, or ammonia, directly to the water supply so that pathogenic organisms are destroyed. Alternatively, microorganisms may be destroyed by a process, such as heating or treatment with ultraviolet light, or microorganisms may be physically removed from the water by filtration. When a chemical disinfectant is used, it is often desirable to remove the disinfectant from the water prior to consumption, and this may be accomplished in a number of ways including chemical neutralization and removal by filtration.
Filtration is used to remove suspended matter from a water supply but may also aid in the removal of dissolved or colloidal species. Filters may be structured from a variety of materials including particulate matter such as sand, diatomaceous earth, or granular activated carbon (GAC), or may be based on a membrane that may be composed of a number of different materials including polymers and fibrous materials. Filters typically work by preventing the passage of suspended material while allowing water to pass through. One way of rating a filter is by its “pore size” which provides information as to what size particle will be retained by the filter. Some methods, such as hyperfiltration, may have pore sizes small enough to exclude some dissolved species.
Water may be adversely affected by the presence of calcium or magnesium ions. Known as “hardness,” a high concentration of these cations, typically more than 200 ppm (mg/L as CaCO3), results in a water that may leave scale or other deposits on equipment and piping. Typically, calcium and magnesium are removed from water (softened) by exchanging the calcium and magnesium ions for alternative cations, often sodium. Water softeners typically contain resin beads that exchange two sodium ions for every calcium or magnesium ion that is removed from the treated water. Periodically, the water softener may be recharged to resupply the resin beads with an adequate supply of sodium or alternative cations.
Reverse osmosis (RO) is a filtration technique that provides for the removal of dissolved species from a water supply. Typically, water is supplied to one side of an RO membrane at elevated pressure and purified water is collected from the low pressure side of the membrane. The RO membrane is structured so that water may pass through the membrane while other compounds, for example, dissolved ionic species, are retained on the high pressure side. Some species however, such as bicarbonate, may not be retained. The “concentrate” that contains an elevated concentration of ionic species may then be discharged or recycled, while the permeate, typically containing a reduced concentration of ionic species, is collected for later use.
A system currently used to purify water for use in beverage production systems is illustrated in FIG. 1. Feed water passes through conduit 150 into particulate filter 110 which helps to remove any particulate matter that may be suspended in the feed water. The water then passes through conduit 151 into pump 140. Pump 140 pressurizes the water which proceeds through conduit 152 into RO device 120. In RO device 120, purified water is collected from the low pressure side of the membrane and passes through conduit 153 to storage tank 130. When an adequate supply of purified water is contained in storage type 130, it may be drawn to a beverage production system through a pump (not shown) connected to conduit 154.
Deionization units may also be used to remove a variety of ionic species from a water supply. Deionization units typically employ either chemical or electrical deionization to replace specific cations and anions with alternative ions. In chemical deionization, an ion exchange resin is employed to replace ions contained in the feed water. The ions on the resin are recharged by periodically passing a recharging fluid through the resin bed. This fluid may be an acid that replenishes the supply of hydrogen ions on the cation exchange resin. For anion exchange resins, the resin may be replenished by passing a base through the resin, replacing any bound anions with hydroxyl groups and preparing the resin for additional anion removal.
In electrodeionization, however, the resin or resins may be replenished by hydrogen and hydroxyl ions that are produced from the splitting of water during the application of electric current to the deionization unit. In continuous electrodeionization (CEDI), the ions are replaced while the feed water is being treated, and thus no separate recharging step is required. Typically, the feed water is first passed through an RO membrane to reduce the total concentration of ionic species present in the feed water. This reduces the load on the CEDI unit and prevents scale and deposits from building up in the concentrating compartment of the unit.